Thermostatic switch



March 10, 1931. BURKHQLDER 1,795,831

THERMOSTATIG SWITCH Filed June 11, 1929 N v ENTO R 774600065 M Buzz/b40152 BY QML 9% ATTORNEY Patented Mar. 10, 1931 UNITED STATES PATENT, OFFICE THEODORE M. BUBKHOLDER, OF BOSTON, MASSACHUSETTS, ASSIGNOB TO ENGINEER- ING- PRODUCTS CORPORATION, OF CAMBRIDGE, MASSACHUSETTS, A CORPORATION OF MASSACHUSETTS Application filed June 11, l

This invention relates to athermostatic switch which is adapted to change its electrical condition upon a slight change of temperature. The switch is especially adapted to be used in conjunction with heating or cooling systems which are to maintan a substantially constant temperature.

In general this invention contemplates the use of the change of vapor pressure of certain liquids for energizing a mercury column to make or break electrical circuits. Switches of this general type have long been known but as a rule are characterized by a physical structure which makes it very hard to handle the devices or adjust them conveniently.

The greatest disadvantages of such prior devices lie in the fact that as a rule the device could not be adjusted to. control a predetermined temperature. Thus a particular switch with a certain amount of mercuryv and liquid might perhaps be adapted to" operate at 75. If it were desired to change the temperature of operation of this device to it was impossible to do so without opening and disturbing the contents thereof. By my invention I am enabled to make the de sired adjustment in a simple and expeditious manner.

Devices of the prior art also sufliered from the disadvantage that when the Vapor pressure of the liquid increased with an increase in tempreature to move the mercury column, the air at the other end of the device was compressed by the moving mercury column, thus creating a back pressure. The result was that the motion of the mercury column was due to the difference in pressures on each end of the column rather than the change of vapor of the volatile liquid only. By my invention the mercury column may change its position without changing the pressure of the air at its free end.

Other advantages such as cheapness of construction, sturdiness and compactness will be apparent as the description proceeds.

The single figure in the drawing'shows an embodiment of my invention. The switch comprises a glass bowl shaped member 1 having an outlet 2 communicating with the air. A long glass tube 5 having its upper end grnnnmos'raa'ro swrron 1929. Serial No. 369,969.

blown out into a spherical chamber 6 is sealed to the upper end of bowl 1 and has a. length 7 projecting downwardly into the bowl. Portion Tina'y be made to-extend as near the bottom of bowl 1 as may be found desirable. Sealed into the walls of tube 1 are a series of elec rical' contacts 12-16 inclusive. These may be disposed in any manner whatsoever. Thus adjacent contacts 'may be disposed in such a manner that unequal temperature differentials will result in opening or closing various sets of contacts.

A quantity of mercury M is shown as partly filling the bowl and rising up into the glass tube" Above this is a quantity of volatile liquid L whosefchange in vapor pressure operates to change the position of the mercury column. IVhile a variety of liquids may be used, I prefer acetone where systems for heating homes are to be controlled. The change in vapor pressure of this liquid is sufficiently great so that a change of two or three degrees .will result in a marked changein the height of the mercury column thus definitely changing the electrical condition of the switch. If desired, however, other liquids such as ether or alcohol may be used. I11 case the temperature range to be controlled is difierent than room temperatures, liquids having different temperature characteristics may be used. lspch liquids may be glycerine, water, and the In the actual filling of the switch with the liquids, a certain amount of mercury and acetone may be poured into the bowl through outlet 2w These amounts do not have to be predetermined to any precise degree and may very easily be guessed at by an ordinary operator. When the two liquids are inside, it is necessary to get the volatile liquid above in the mercury column. In order to do this the device is turned over so that it is horizontal and shaken back and forth in that condition.

This is to get as much mercury and acetone.

into chamber 6 and tube 5 as possible. The device is then turned to its normal position while OlIllGt 2 is left open. The mercury column immediately falls down a definite height with the volatile liquid above it. Some oi the liquid maybe left floating on the mercury in her. perature and the vapor pressure of the acebowl 1 but this evaporates within a short time.

The presence of volatile liquid floating on the mercury surface in bowl 1 would render the device entirely inoperative if an outlet were notprovided. Obviously the vapor ressure above the mercury surface in the bowl would equal the vapor pressure above the mercury column in chamber 6 and tube 5 and would maintain the mercury column stationary. Hence, in devices of the prior art any possibility of the volatile liquid being at both ends of the mercury column would thus render the device completely inoperative. In the course of shipping and rough handling, it is altogether possiblethat same volatile liquid might travel to the other end of the column.

' In order to adjust the height of the mercury column and thus within a certain range adjust 'the temperature at which the contacts will be opened or closed, the entire device may be tilted from the vertical position just enough to allow air to bubble up through and drop the column. If it is found that the column is too low, the entire tube may be turned upside down and air pumped out by the mercury. hen the device is restored to its normal position it will be found that the mercury column is higher.

A. switch of this type may be caused to move the mercury column an appreciable amount by merely touching the upper cham- The heat of the hand raises the temtone which results in the mercury column being forced downwardly. In actual prac- "tice a device of this character usually has its 1 outlet closed by a porous plug 20 of reed or the like. In this way the entire switch'may be easily changed without loss of contents.

It is evident that'with a porous member closing outlet 2 the air pressure within bowl 1 above the mercury is at all times equal to the pressure of the atmosphere. Any increase in tempeiature .tending to increase the vapor pressu e of the liquid in chamber 6 will therefore depress the mercury column. In moving downwardly the level of the mercury rises in bowl 1 and forces some air through the porous plug. If side member 2 were sealed, it isv evident that when the vapor pressure of the volatile liquid in 6 increased that the depression of the mercury column would" compress the air in chamber 1. This back pressure. would detract from the effectivenessof' the device. Furthermore, with the increase in temperature, the temperature of the air in the bowl would increase with a resultant increase in pressure. Hence, the pressure above the surface of the mercury in bowl 1 would not only be increased by compression but also by depression of mer- 2. A thermostatic switch comprising a closed glass bowl having an outlet, a porous member closing said outlet, a vertical tube having an enlarged chamber at one end sealed to the top of said bowl, said tube having-a depending portion extending into the bowl and almost reaching the bottom thereof, a plurality of electrical contacts sealed in said vertical tube, a quantity of mercury in said bowl and in said tube, a quantity of acetone floating on said mercury in said tube.

3. A thermostatic switch comprising a closed glass bowl communicating with the atmosphere through a porous member, a vertical tube having a closed end sealed at the top of said bowl and having aportion de pending therein, a plurality of electrical contacts sealed in said vertical tube above the bowl, a quantity of mercury in said bowl and in said tube, and a quantity of volatile liquid floating on said mercury in said tube.

THEODORE M. BURKHOLDER.

cury if-t-he outlet were sealed. By having I the outlet communicate with the atmosphere,

1t 15 evident therefore that the free and full 1 

